Electrostatic chucks are widely used to hold substrates, such as semiconductor wafers, in stationary position during substrate processing in processing chambers used for various applications, such as physical vapor deposition, etching, or chemical vapor deposition. Typically, electrostatic chucks contain one or more electrodes embedded within a dielectric material such as ceramic. As power is applied to the electrode, an attractive force is generated between the electrostatic chuck and the substrate disposed thereon.
The attractive force is commonly generated through either a Coulombic or a Johnsen-Rahbek effect. Generally, electrostatic chucks utilizing Coulombic attraction have electrodes disposed in bodies having high resistivities. The insulating properties of the body maintain a capacitive circuit (i.e., charge separation) between the electrodes and the substrate when an electrical potential is applied between them. Electrostatic chucks utilizing Johnsen-Rahbek attraction have electrodes disposed in bodies having lower resistivities which allow charge migration through the body when power is applied to the electrodes.
Charges (i.e., electrons) within the body migrate to portions of the surface of the electrostatic chuck making contact with the substrate when voltage is applied to the electrodes. Some minimal current passes between the chuck surface and the substrate at the contact point but generally not enough to result in device damage. Thus, as the charges accumulate at both sides of the contact points, a highly localized and powerful electric field is established between the substrate and electrostatic chuck. Since the attractive force is proportional to the distance between the opposite charges, the substrate is secured to the chuck with less power than necessary in chucks comprising high resistivity material (i.e., chucks having solely Coulombic attraction) as charge accumulates on the chuck's support surface close to the substrate.
As electrostatic chucks generally rely on the electric potential developed between the embedded electrodes and the substrate for the generation of attractive force, prevention of current leakage through the chuck body is important. For example, in a Johnsen-Rahbek electrostatic chuck, plasma may contact the surface of the electrostatic chuck. As the plasma provides a current path between the electrostatic chuck and the chamber sidewalls that are normally grounded, the movement of charge through the body is diverted from the support surface to ground, substantially reducing the charge accumulation on the support surface resulting in diminished or lost attractive force. As the attractive force is decreased or lost, the substrate may move or become dislodged. A dislodged substrate is likely to become damaged or improperly processed. Current leakage from this or other reasons through the sides or bottom of the electrostatic chuck has a similar effect.
Problems associated with a Johnsen-Rahbek type electrostatic chuck include, for example, undesired leakage current, variation in electrostatic attraction force depending on the type of substrate being held by the electrostatic chuck, and difficulty in detaching the substrate from the electrostatic chuck, i.e., de-chucking, after removing the power supply.
Problems associated with a Coulombic type electrostatic chuck include, for example, insufficient resistance to erosive and corrosive conditions, e.g., corrosive gases, such as those that exist in semiconductor device manufacture.
Therefore, a need exists for improved electrostatic chucks having reduced leakage current and improved chucking and de-chucking performance through the operational life of the electrostatic chuck. Also, a need exists for electrostatic chucks having improved erosion and corrosion resistance in severe conditions, e.g., plasma, such as those that exist in semiconductor device manufacture.